JSON输出到Python字典-理解困难

Question

New to JSON and Python. I successfully call and can get an output using something like this

def lendbook(currency='xtl'): #GET /lendbook/:currency

    r = requests.get(URL + "/lendbook/" + currency, verify=False)
    rep = r.json()

    return rep

print lendbook()

The data prints out fine but a real muddle for a new beginner. A sample is below from the Python console

{u'bids': [{u'timestamp': u'1405112154.0', u'rate': u'0.365', u'frr': u'No', u'amount': u'20.0', u'period': 30}], u'asks': [{u'timestamp': u'1405143214.0', u'rate': u'1.9345', u'frr': u'No', u'amount': u'0.72115369', u'period': 2}, {u'timestamp': u'1401975696.0', u'rate': u'2.0', u'frr': u'Yes', u'amount': u'0.53', u'period': 30}, {u'timestamp': u'1405011490.0', u'rate': u'2.0', u'frr': u'Yes', u'amount': u'3.44796922', u'period': 30}, {u'timestamp': u'1405137594.0', u'rate': u'2.0', u'frr': u'Yes', u'amount': u'0.12279759', u'period': 2}, {u'timestamp': u'1405139396.0', u'rate': u'2.0', u'frr': u'Yes', u'amount': u'1.84883351', u'period': 2}, {u'timestamp': u'1405140302.0', u'rate': u'2.0', u'frr': u'Yes',

Obviously I want to format the date and in fact really only after the rate and period. What looping structure for dictionaries should I use as when I use a FOR loop I only seem to return the words 'bids' and 'asks'. There is obviously another structure in the dictionary I am not understanding?

Really appreciate help as I get my head around JSON and Python dictionaries

Answer 1

When you loop through a dictionary, you only loop through its keys using basic for loop.

Change that to for key, value in dict.iteritems(): .

>>> obj = {'bids': [1000, 2999], 'asks': [4, 5]}
>>> for key, value in obj.iteritems():
...     print key, value
... 
bids [1000, 2999]
asks [4, 5]
>>> 

Answer 2

Print the type of the data using type(). This way you can know the type of data in the json & process it step by step.

Answer 3

Seems like the JSON object you are getting in return contains objects(lists) (ie, "bids", and "asks") So I guess you are confused as to why you aren't accessing the values. I suggest you first get a hold of the object you are interested in (say "bids");

bidsList = rep['bids']

As you can see that "bids" is a list of objects([] >> indicates). You can now iterate.

#[{'timestamp': '1405112154.0', 'rate': '0.365', 'frr': 'No', 'amount': '20.0', 'period': 30}]
>>> bidsList = rep['bids']
>>> for obj in bidsList:
>>>   print obj
... 
{'timestamp': '1405112154.0', 'rate': '0.365', 'frr': 'No', 'amount': '20.0', 'period': 30}

You can get the values like,

>>> for obj in bidsList:
>>>   print obj['timestamp']
....
1405112154.0 
>>>

I suggest you create classes named Bids, Asks and any other object type you know is returned in that JSON object of yours. You can then access the object (rep['theObject']) and create instance of Bids(pass the json object to it and get an instance) It will save you from all this as the logic of getting the object would go in the class itself. Better design I would say.

Also(let's just say you want to stick to this approach), if you don't want to hardcode things, say you want to write a code that is independent of what is returned in the JSON. In that case you can Iterator over the Dict returned ('rep') in your case and for every object that you get in an iteration, you check the type, if it is a dict itself, then you do the same for it (iterator over the keys), or if it is a list, you iterate like I mentioned, otherwise access the values through the keys.

Hope this helps!